GPS-X Technical Reference

Tools Object 350
Manipulated Variable Parameters
Manipulated variable w/o label: This is the manipulated variable name without the
stream label.
Label of manipulated variable: This is the stream label of the manipulated variable.
Value of manipulated variable: This is the initial value of the manipulated variable.
Minimum value: This is the lower bound on the manipulated variable.
Maximum value: This is the upper bound on the manipulated variable.
Tuning PID Controllers
Many different techniques exist for tuning PID controllers. While an in-depth discussion
of these techniques is beyond the scope of this manual, some general guidelines are
provided below.
A simple and conservative approach to controller tuning is as follows:
Start with a small proportional gain and a large integral time; set the derivative
time to zero (0). As a rough rule of thumb:
o Use a value of 0.5/K p as a starting value for the proportional gain (K p is
the steady-state process gain, defined as the change in the controlled
variable at steady-state for a one-unit change in the manipulated
variable).
o Use a value of 1.5t as a starting point for the integral time (t is the time
constant of the first-order response that most closely approximates the
controlled variable response to a step in the manipulated variable).
Gradually increase the proportional gain until further increases result in
deterioration in control performance.
Gradually decrease the integral time until further decreases result in deterioration
in control performance.
Gradually increase the derivative time.
Fine-tune the parameters as needed.
A facility for tuning PID controllers based on the Ciancone correlations for setpoint
changes is available for all PID controllers in GPS-X. The PID tuning parameters
calculated using the Ciancone correlations are based on estimates of the process gain,
dead time, and time constant, obtained by a least-squares fit of the time series data
collected under tuning mode.
GPS-X Technical Reference